1. Field of Invention
The present invention relates to a magnetic head for floppy disc drive.
2. Background of Related Art
Since, in general, a FDD (a floppy disc drive) is mounted in a personal computer, a magnetic head of the FDD is apt to generate a reading error due to an electromagnetic noise from a CRT or a switching electric source and so on. And, for preventing such a reading error of the magnetic head from being generated, it is a general tendency to shield the magnetic head with a magnetic material having a high permeability such as permalloy or ferrite (this general magnetic head is hereinafter referred to, for convenience sake, as a conventional example 1).
By the way, recently, in a note PC and such (a note-type of personal computer), low-profile FDD having a thickness of half-inch size has been used, and in this case, it has been difficult to shield a magnetic head with a magnetic material having a high permeability such as permalloy or ferrite. As a countermeasure, there is what is disclosed in JP Patent Laid-open Application No. Hei 7-235013 (hereinafter for convenience, referred to as a conventional example 2).
A magnetic head 1 of the conventional example 2, as shown in FIG. 6, comprises a front core 3, a back yoke 5 and a later described read/write coil 6 and an erasing coil 7. The front core 3 consists of a front chip core 2 having a read/write gap G1 and an erasing gap G2 and a first and a second sliders 4a and 4b of non-magnetic material which are integrated with the front chip core 2 slides on a magnetic recording medium (not shown). The one side (upper in FIG. 6) of the front core 3 slides on a magnetic recording medium (not shown). The back yoke 5 is made of a magnetic material having a high permeability such as Mn-Zn ferrite and bonded to the outer side of the front core 3.
The back yoke 5 is formed in the shape of approximately a hollow square pillar outer-body 8, a tip end of which is bonded to the above mentioned front core 3, a bottom portion 9 formed at the proximal side of the outer-body 8 and three approximately similarly shaped leg portions 10a, 10b and 10c (hereinafter referred to, for convenience sake, as the first leg portion, the second leg portion and the third leg portion viewing from right to left in FIG. 6) which stand upright in juxtaposing on the bottom portion 9 and forms a closed magnetic circuit with the front chip core 2 and the bottom portion 9 by being bonded to the front chip core 2 with the tip ends of the leg portions.
The outer-body 8 is formed in the shape of approximately a hollow square pillar with two opposing short sides (hereinafter referred to, for convenience sake, as a first short side 8.sub.1 1 shown at right lower portion in FIG. 6 and a second short side 8.sub.1 2 shown at left upper portion therein) and two opposing long sides (hereinafter referred to, for convenience sake, as a first long side 8.sub.2 1 shown at right upper portion in FIG. 6 and a second long side 8.sub.2 2 shown at left lower portion therein) and between the first short side 8.sub.1 1 and the first leg portion 10a and between the second short side 8.sub.1 2 and the third leg portion 10c on the bottom portion 9 respectively, an opening 11 is formed. From the opening 11 a lead wire 6a of the read/write coil 6 and a lead wire 7a of the erasing coil 7 are drawn out and connected to outer connecting terminals of such as not shown FPC (flexible print board).
The above-mentioned first and third leg portions 10a and 10c are inserted in the above mentioned read/write coil 6 and the erasing coil 7.
The back yoke 5 of this magnetic head 1 of the conventional example 2 is made of the magnetic material having a high permeability such as Mn-Zn ferrite and its outer-body 8 and the bottom portion 9 function in magnetic shielding. And in this case, since the back yoke 5 provided on the magnetic head 1 carries out magnetic shielding, a problem which has the difficulty of the magnetic shielding which is apt to be generated in the case of being used in the low-profile FDD can be planned to be improved.
By the way, the back yoke 5 is formed, as well as in forming method of any ceramics, in such a manner as, after powders of the Mn-Zn ferrite and such are mixed with any binder, which are molded in a given shape by using a mold, that molded product is sintered at a high temperature thereby to obtain a burnt-solidified product. Accordingly, there is an anxiety of generation of bending or any crack after sintering in the case of slimmer leg portions (10a, 10b and 10c).
To the contrary, in the magnetic head 1 of the conventional example 2above mentioned, although the diameter of the first and the third leg portions 10a, 10c which are inserted in coils (the read-write coil 6 and the erasing coil 7) is necessary to make it slimmer comparing with the inner diameter of the coil, however, since there is no such limitation as to the second leg portion 10b which is not coupled with the coil, the diameter thereof is not necessarily made approximately similar with the first leg portion 10a and the third leg portion 10c. However, in the magnetic head 1 of the conventional example 2, since, even though the diameter of the first leg portion 10a and the third leg portion 10c is slimmer compared with the coil diameter, they are reinforced by the coupling of the coil and prevented from being broken, on the other hand the diameter of the second leg portion 10b is made approximately similar (approximately similar shape) with the first and third leg portions 10a and 10c, to that extent the strength of the second leg portion 10b becomes weak relatively, so that there was in fact the above problem i.e. anxiety of generation of bending and crack.
For that reason, there was not an appropriate improvement or countermeasure against such problem as the magnetic head 1 of the conventional example 2 has concerning the difficulty of providing magnetic shielding, which can be generated when used in a low-profile FDD.
Now, to the contrary to the conventional example 2 (FIG. 6), as one of the conventional example where the first, second and third leg portions 10a, 10b and 10c are made slimmer by a post-working (hereinafter referred to as "the third embodiment"), what is disclosed in JP Patent Laid-open No. Hei 10-40525 (hereinafter referred to, for convenience sake, as "the conventional example 3").
The magnetic head 1 of the conventional example 3, as shown in FIGS. 7 and 8, is provided with a front core 3 which is formed with the slider 4 and the front chip core 2 by coupling the front chip core 2 with a hole 12 formed on the slider 4, and the back yoke 5 which is made of a high permeability magnetic material which is formed as following process.
The back yoke 5, compared with the back yoke 5 of the above conventional example 2, is different in the structure in the points that the opening 11 is not formed on the bottom portion 9, that, on the second long side 8.sub.2 2, the first projection 13a, second projection 13b and third projection 13c are formed in such a manner as those are extended toward the first leg portion 10a, the second leg portion 10b and the third leg portion 10c respectively and that a cut-out 14 is formed on the first short side 8.sub.1 1 and the second short side 8.sub.1 2.
And, in this back yoke 5, at the time of powder-molding and sintering, as shown in a dotted line 15 in FIG. 7, the first, second and third leg portions 10a, 10b and 10c are bonded to the outer-body 8 (the first, second and third projections 13a, 13b and 13c) and by a later post-working such as grooving work by cutting the dotted portion 15 in FIG. 7 to remove that portion, the first, second and third leg portions 10a, 10b and 10c are separated at a given width (thickness). By this cut-grooving, the cut-out 14 is formed on the first and second short sides 8.sub.1 1 and 8.sub.1 2. Through this cut-out 14, the lead wire 6a of the read/write coil 6 and the lead wire 7a of the erasing coil 7a are drawn out.
In this magnetic head 1 of the conventional example 3, its the first leg portion 10a, the second leg portion 10b and third leg portion 10c are bonded to the outer-body 8 at the time of being powder-molded and being sintered, thereby the generation of any bending or crack is prevented.
However, in the magnetic head 1 of the above conventional example 3 has the drawback in which, when working the first leg portion 10a, the second leg portion 10b and the third leg portion 10c by cutting into a given thickness, since not only the first leg portion 10a and the third leg portion 10c but also the second leg portion 10b which is not inserted in the coil is cut to the thickness similar to the first and third leg portions, to that extent the magnetic resistance of the magnetic head becomes large.
Further, since the first leg portion 10a and the third leg portion 10c are inserted in the coils (the read/write coil 6 and the erasing coil 7) and fixed with epoxy adhesives and such, the first and third leg portions 10a and 10c are in the state reinforced with coils (the read/write coil 6 and the erasing coil 7), thereby those are adapted to have the strength to resist sufficiently against any shock and the like during assembling or using to prevent them from being broken. However, since the second leg portion 10b is not inserted in the coil, the strength is maintained small and apt to be broken by any shock during assembling or using.